Circuit-breakers having two interrupting chambers per pole commonly contain both a fixed portion comprising main contacts, arcing contacts, and a blast piston, and also a moving portion comprising main contacts and arcing contacts, and a blast cylinder. In a variant, the piston is placed on the moving portion, the cylinder then being fixed. The moving portion is moved on circuit-breaker disengagement or engagement by means of rods connected via a linkage to a drive rod moved by a control system placed at the bottom of the column supporting the two interrupting chambers.
The drive energy required for disengagement is proportional to the mass of the moving parts and to the square of the relative speed of separation of the contacts. The relative speed of contact separation is imposed mainly by the characteristics of the current to be interrupted, and by the pressure of the insulation gas. The control energy may be reduced by reducing the mass of the moving parts, but such reductions are unavoidably limited by the need to provide equipment that is robust and reliable.
The idea underlying the present invention is that the energy can be reduced if the disengagement speed is halved, with this being done by imparting the same speed simultaneously both to the moving assembly and to the "fixed" assembly, which same speed is equal to half of the above-mentioned relative speed of contact separation. It can then be understood that the assembly that is usually fixed in each of the interrupting chambers must be made "semi-moving", and both the moving assembly and the semi-moving assembly must be provided with means for being driven in opposite directions and with opposite velocities on disengagement.
It is known that the voltage across the terminals of each of the chambers of the pole is generally not equal to half of the total voltage of the line. Usually, the voltage of the line is distributed in proportions in the vicinity of 70% and 30%. In order to avoid over-dimensioning the chambers so as to make it possible to interrupt voltages greater than half the line voltage, it is well known to dispose voltage-distributing capacitors referred to as "balancing" capacitors in parallel with each interrupting chamber. Such capacitors are generally placed in ceramic columns disposed above the interrupting chambers. Such columns are costly.